Purified Hydrogen Peroxide Gas Microbial Control Methods and Devices

ABSTRACT

The present invention relates to methods and devices for providing microbial control and/or disinfection/remediation of an environment. The methods generally comprise: generating a Purified Hydrogen Peroxide Gas (PHPG) that is substantially free of, e.g., hydration, ozone, plasma species, and/or organic species; and directing the gas comprising primarily PHPG into the environment such that the PHPG acts to provide microbial control and/or disinfection/remediation in the environment, preferably both on surfaces and in the air.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 17/194,592, filed Mar. 8, 2021, (now allowed), which is acontinuation application of U.S. application Ser. No. 16/177,592, filedNov. 1, 2018, (now U.S. Pat. No. 10,940,223), which is a continuationapplication of U.S. application Ser. No. 15/175,355, filed Jun. 7, 2016(now U.S. Pat. No. 10,188,766)), which is a continuation of U.S.application Ser. No. 14/671,074, filed Mar. 27, 2015 (now U.S. Pat. No.9,370,592, issued Jun. 21, 2016), which is a continuation application ofU.S. application Ser. No. 14/175,551, filed Feb. 7, 2014 (now U.S. Pat.No. 9,034,255, issued May 19, 2015), which is a continuation applicationof U.S. application Ser. No. 13/425,736, filed Mar. 21, 2012 (now U.S.Pat. No. 8,685,329, issued Apr. 1, 2014), which is a divisionalapplication of U.S. application Ser. No. 12/187,755, filed Aug. 7, 2008(now U.S. Pat. No. 8,168,122, issued May 1, 2012), which claims priorityto U.S. Provisional Application No. 60/954,566, filed Aug. 7, 2007(expired), and U.S. Provisional Application No. 61/031,580, filed Feb.26, 2008 (expired), each of which is hereby incorporated by reference intheir entireties.

FIELD OF INVENTION

The present invention generally relates to infection and microbialcontrol methodologies and devices related thereto.

BACKGROUND OF INVENTION

Pathogenic microbes, molds, mildew, spores, and organic and inorganicpollutants are commonly found in the environment. Microbial control anddisinfection in environmental spaces is desirable to improve health.Numerous ways have been used to in the past in an attempt to purify airand disinfect surfaces. For example, it is already known that ReactiveOxidizing Species (ROS) produced by, e.g., photocatalytic oxidationprocess can oxidize organic pollutants and kill microorganisms. Moreparticularly, hydroxyl radical, hydroperoxyl radicals, chlorine andozone, end products of the photocatalytic reaction, have been known tobe capable of oxidizing organic compounds and killing microorganisms.However, there are limitations to the known methods and devices, notonly due to efficacy limitation but also due to safety issues.

ROS is the term used to describe the highly activated air that resultsfrom exposure of ambient humid air to ultraviolet light. Light in theultraviolet range emits photons at a frequency that when absorbed hassufficient energy to break chemical bonds. UV light at wavelengths of250-255 nm is routinely used as a biocide. Light below about 181 nm, upto 182-187 nm is competitive with corona discharge in its ability toproduce ozone. Ozonation and UV radiation are both being used fordisinfection in community water systems. Ozone is currently being usedto treat industrial wastewater and cooling towers.

Hydrogen peroxide is generally known to have antimicrobial propertiesand has been used in aqueous solution for disinfection and microbialcontrol. Attempts to use hydrogen peroxide in the gas phase, however,have previously been hampered by technical hurdles to the production ofPurified Hydrogen Peroxide Gas (PHPG). Vaporized aqueous solutions ofhydrogen peroxide produce an aerosol of microdroplets composed ofaqueous hydrogen peroxide solution. Various processes for “drying”vaporized hydrogen peroxide solutions produce, at best, a hydrated formof hydrogen peroxide. These hydrated hydrogen peroxide molecules aresurrounded by water molecules bonded by electrostatic attraction andLondon Forces. Thus, the ability of the hydrogen peroxide molecules todirectly interact with the environment by electrostatic means is greatlyattenuated by the bonded molecular water, which effectively alters thefundamental electrostatic configuration of the encapsulated hydrogenperoxide molecule. Further, the lowest concentration of vaporizedhydrogen peroxide that can be achieved is generally well above the 1.0ppm OSHA workplace safety limit, making these processes unsuitable foruse in occupied areas.

Photocatalysts that have been demonstrated for the destruction oforganic pollutants in fluid include but are not limited to TiO₂, ZnO,SnO₂, WO₃, CdS, ZrO₂, SB₂O₄ and Fe₂O₃. Titanium dioxide is chemicallystable, has a suitable bandgap for UV/Visible photoactivation, and isrelatively inexpensive. Therefore, photocatalytic chemistry of titaniumdioxide has been extensively studied over the last thirty years forremoval of organic and inorganic compounds from contaminated air andwater.

Because photocatalysts can generate hydroxyl radicals from adsorbedwater when activated by ultraviolet light of sufficient energy, theyshow promise for use in the production of PHPG for release into theenvironment when applied in the gas phase. Existing applications ofphotocatalysis, however, have focused on the generation of a plasmacontaining many different reactive chemical species. Further, themajority of the chemical species in the photocatalytic plasma arereactive with hydrogen peroxide, and inhibit the production of hydrogenperoxide gas by means of reactions that destroy hydrogen peroxide. Also,any organic gases that are introduced into the plasma inhibit hydrogenperoxide production both by direct reaction with hydrogen peroxide andby the reaction of their oxidized products with hydrogen peroxide.

The photocatalytic reactor itself also limits the production of PHPG forrelease into the environment. Because hydrogen peroxide has greaterchemical potential than oxygen to be reduced as a sacrificial oxidant,it is preferentially reduced as it moves downstream in photocatalyticreactors as rapidly as it is produced by the oxidation of water.

Oxidation

2 photons+2H₂O→2OH*+2H⁺+2e ⁻

2OH*→H₂O₂

Reduction

H₂O₂+2H⁺+2e ⁻→2H₂O

Additionally, several side reactions generate a variety of species thatbecome part of the photocatalytic plasma, and which inhibit theproduction of PHPG for release into the environment as noted above.

The wavelengths of light used to activate photocatalysts are alsoenergetic enough to photolyze the peroxide bond in a hydrogen peroxidemolecule and are also an inhibitor in the production of PHPG for releaseinto the environment. Further, the practice of using wavelengths oflight that produce ozone introduces yet another species into thephotocatalytic plasma that destroys hydrogen peroxide.

O₃±H₂O₂→H₂O+2O₂

In practice, photocatalytic applications have focused on the productionof a plasma, often containing ozone, used to oxidize organiccontaminants and microbes. Such plasmas are primarily effective withinthe confines of the reactor itself, by nature have limited chemicalstability beyond the confines of the reactor, and actively degrade thelimited amounts of hydrogen peroxide gas that they may contain. Further,because the plasma is primarily effective within the reactor itself,many designs maximize residence time to facilitate more completeoxidation of organic contaminants and microbes as they pass through thereactor. Since hydrogen peroxide has such a high potential to bereduced, the maximized residence time results in minimized hydrogenperoxide output.

Also, most applications of photocatalysis produce environmentallyobjectionable chemical species. First among these is ozone itself, anintentional product of many systems. Further, since organic contaminantsthat pass through a reactor are seldom oxidized in one exposure,multiple air exchanges are necessary to achieve full oxidation to carbondioxide and water. As incomplete oxidation occurs, a mixture ofaldehydes, alcohols, carboxylic acids, ketones, and other partiallyoxidized organic species is produced by the reactor. Often,photocatalytic reactors can actually increase the overall concentrationof organic contaminants in the air by fractioning large organicmolecules into multiple small organic molecules such as formaldehyde.

In summary, the production of PHPG for release into the environment isnot achieved in the prior art. Methods of vaporizing aqueous hydrogenperoxide solutions produce, at best, hydrated forms of hydrogenperoxide. Also, though photocatalytic systems are capable of producinghydrogen peroxide, they have multiple limitations that severely inhibitPHPG production for release into the environment.

SUMMARY OF THE INVENTION

In one aspect of the invention, a method of providing microbial controland/or disinfection/remediation of an environment is disclosed. Themethod generally comprises (a) providing a photocatalytic cell thatpreferentially produces hydrogen peroxide gas; (b) generating a PurifiedHydrogen Peroxide Gas (PHPG) that is substantially free of, e.g.,hydration, ozone, plasma species, and/or organic species; and (c)directing the gas comprising primarily PHPG into the environment suchthat the PHPG acts to provide microbial control and/ordisinfection/remediation in the environment, preferably both on surfacesand in the air.

In certain embodiments, the method comprises (a) exposing a metal, ormetal oxide, catalyst to ultraviolet light in the presence of humid,purified ambient air under conditions so as to form Purified HydrogenPeroxide Gas (PHPG) that is substantially free of, e.g., hydration,ozone, plasma species, and/or organic species; and (b) directing thePHPG into the environment such that the hydrogen peroxide gas acts toprovide infection control and/or disinfection/remediation in theenvironment, preferably both on surfaces and in the air.

Another aspect of the invention relates to a diffuser apparatus forproducing PHPG that is substantially free of, e.g., hydration, ozone,plasma species, and/or organic species. The diffuser apparatus generallycomprises: (a) a source of ultraviolet light; (b) a metal oxide catalystsubstrate structure; and (c) an air distribution mechanism.

Another aspect of the invention relates to the oxidation/removal ofVOC's from ambient air by PHPG once it is released into the environment.

Another aspect of the invention relates to the removal of ozone fromambient air by PHPG once it is released into the environment.

These and other aspects of the invention will become apparent to thoseskilled in the art upon reading the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section of a particular embodiment of a diffuserapparatus of the present invention

FIG. 2 is a cut away view of a particular embodiment of a diffuserapparatus of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates generally to microbial control and/ordisinfection/remediation methods and devices related thereto. In certainembodiments, photocatalytic processes may be utilized in the methods anddevices described herein.

The fundamental nature of a photocatalytic process is to create activeintermediates in a chemical reaction by absorption of light. This occurswhen a photon of the appropriate wavelength strikes the photocatalyst.The energy of the photon is imparted to a valence band electron,promoting the electron to the conduction band, thus leaving a “hole” inthe valence band. In the absence of an adsorbed chemical species, thepromoted electron will decay and recombine with the valence band hole.Recombination is prevented when the valence band hole captures anelectron from an oxidizable species—preferentially molecularwater—adsorbed to an active surface site on the photocatalyst.Concurrently, a reducible species adsorbed on the catalystsurface—preferentially molecular oxygen—may capture a conduction bandelectron.

Upon initiation of the photocatalytic process, or at the entrance pointof a photocatalytic reactor, the following reactions occur.

Oxidation

2 photons+2H₂O→2OH*+2H⁺+2e ⁻

2OH*→H₂O₂

Reduction

H₂O₂+2H⁺+2e ⁻→2H₂O

Once hydrogen peroxide has been produced, however, the photocatalystpreferentially reduces hydrogen peroxide instead of molecular oxygen,and the reaction shifts to the following equilibrium which takes placewithin the majority of the reactor volume.

Oxidation

2 photons+2H₂O→2OH*+2H⁺+2e ⁻

2OH*→H₂O₂

Reduction

H₂O₂+2H⁺+2e ⁻→2H₂O

In the context of the present invention, Purified Hydrogen Peroxide Gas(PHPG) may be produced using a photocatalytic process with apurpose-designed morphology that enables the removal of hydrogenperoxide from the reactor before it is forced to undergo subsequentreduction by the photocatalyst. Denied ready availability of adsorbedhydrogen peroxide gas, the photocatalyst is then forced topreferentially reduce oxygen, rather than hydrogen peroxide. Hydrogenperoxide gas may then generally be produced simultaneously by both theoxidation of water and the reduction of dioxygen in the photocatalyticprocess. Without intending to be limited, in operation the amount ofhydrogen peroxide produced may be doubled, then removed from the systembefore the vast majority of it can be reduced—thereby resulting in anoutput of PHPG that is up to 150 times greater than the incidentaloutput of unpurified hydrogen peroxide from standard photocatalyticreactors under the same conditions. In the purpose-designed morphologythe dominant reactions become:

Oxidation

2 photons+2H₂O→2OH*+2H⁺+2e ⁻

2OH*→H₂O₂

Reduction

H₂O₂+2H⁺+2e ⁻→2H₂O

However, without being limited by theory, it should be noted that themicrobial control and/or disinfection/remediation methods and devices ofthe invention are not achieved as a result of the photocatalyticprocess, but by the effects of PHPG once it is released into theenvironment.

Using morphology that permits immediate removal of hydrogen peroxide gasbefore it can be reduced, PHPG may be generated in any suitable mannerknown in the art, including but not limited to, any suitable processknown in the art that simultaneously oxidizes water in gas form andreduces oxygen gas, including gas phase photo-catalysis, e.g., using ametal catalyst such as titanium dioxide, zirconium oxide, titaniumdioxide doped with cocatalysts (such as copper, rhodium, silver,platinum, gold, etc.), or other suitable metal oxide photocatalysts.PHPG may also be produced by electrolytic processes using anodes andcathodes made from any suitable metal, or constructed from metal oxideceramics using morphology that permits immediate removal of hydrogenperoxide gas before it can be reduced. Alternatively, PHPG may beproduced by high frequency excitation of gaseous water and oxygenmolecules on a suitable supporting substrate using morphology thatpermits immediate removal of hydrogen peroxide gas before it can bereduced.

In one aspect of the invention, a method of providing microbial controland/or disinfection/remediation of an environment is disclosed. Themethod generally comprises (a) generating a gas comprised of PurifiedHydrogen Peroxide Gas (PHPG) that is substantially free of, e.g.,hydration, ozone, plasma species, and/or organic species; and (b)directing the gas comprised of PHPG into the environment such that thePHPG acts to provide microbial control and/or disinfection/remediationin the environment, preferably both on surfaces and in the air.

In certain embodiments, the method comprises (a) exposing a metal, ormetal oxide, catalyst to ultraviolet light in the presence of humidpurified ambient air under conditions so as to form Purified HydrogenPeroxide Gas (PHPG) that is substantially free of, e.g., hydration,ozone, plasma species, and/or organic species; and (b) directing thePHPG into the environment such that the PHPG acts to provide infectioncontrol and/or disinfection/remediation in the environment, preferablyboth on surfaces and in the air, removal of ozone from the ambient air,and removal of VOC's from the ambient air.

In one embodiment, the ultraviolet light produces at least onewavelength in a range above about 181 nm, above about 185 nm, aboveabout 187 nm, between about 182 nm and about 254 nm, between about 187nm and about 250 nm, between about 188 nm and about 249 nm, etc

Another aspect of the invention relates to a diffuser apparatus forproducing Purified Hydrogen Peroxide Gas (PHPG) that is substantiallyfree of, e.g., hydration, ozone, plasma species, and/or organic species.With reference to FIGS. 1 and 2, the diffuser apparatus generallycomprises: (a) a source of ultraviolet light 4; (b) a metal or metaloxide catalyst substrate structure 3; and (c) an air distributionmechanism 5, 6, and/or 7.

The air distribution mechanism may be a fan 5 or any other suitablemechanism for moving fluid, e.g., air, through the diffuser apparatus.In accordance with certain aspects of the invention, the selection,design, sizing, and operation of the air distribution mechanism shouldbe such that the fluid, e.g. air, flow through the diffuser apparatus isgenerally as rapid as is practical. Without intending to be limited bytheory, it is believed that optimal levels of PHPG are generated forexiting the diffuser apparatus under rapid fluid flow conditions.

The ultraviolet light source 4 may generally produce at least one rangeof wavelengths sufficient to activate photocatalytic reactions of thehumid ambient air, but without photolyzing oxygen so as to initiate theformation of ozone. In one embodiment, the ultraviolet light produces atleast one wavelength in a range above about 181 nm, above about 185 nm,above about 187 nm, between about 182 nm and about 254 nm, between about187 nm and about 250 nm, between about 188 nm and about 249 nm, etc.Such wavelengths will generally produce PHPG including hydrogen peroxidein the substantial absence of ozone.

In accordance with the present invention, the term “substantial absenceof ozone” generally means amounts of ozone below about 0.015 ppm, downto levels below the LOD (level of detection) for ozone. Such levels arebelow the generally accepted limits for human health. In this regard,the Food and Drug Administration (FDA) requires ozone output of indoormedical devices to be no more than 0.05 ppm of ozone. The OccupationalSafety and Health Administration (OSHA) requires that workers not beexposed to an average concentration of more than 0.10 ppm of ozone for 8hours. The National Institute of Occupational Safety and Health (NIOSH)recommends an upper limit of 0.10 ppm of ozone, not to be exceeded atany time. EPA's National Ambient Air Quality Standard for ozone is amaximum 8 hour average outdoor concentration of 0.08 ppm.

In certain embodiments the PHPG may, however, be used for the removal ofozone from the ambient environment by means of the following reaction:

O₃±H₂O₂→H₂O+2O₂

In certain embodiments the PHPG may be used for the removal of VOC'sfrom the ambient environment by means of direct oxidation of VOC's bythe PHPG.

In certain embodiments, the PHPG may be used for microbial control,including but not limited to, as a biocide, for indoor air treatment, asa mold and/or fungus eliminator, as a bacteria eliminator, and/or as aneliminator of viruses. The PHPG method may produce hydrogen peroxide gassufficient to carry out a desired microbial control and/ordisinfection/remediation process. A sufficient amount is generally knownby those skilled in the art and may vary depending on the solid, liquid,or gas to be purified and the nature of a particulardisinfection/remediation.

In certain embodiments, with reference to the microbial control and/ordisinfection/remediation of air and related environments (includingsurfaces therein), the amount of PHPG may vary from about 0.005 ppm toabout 0.10 ppm, more particularly, from about 0.02 ppm to about 0.05ppm, in the environment to be disinfected. Such amounts have been proveneffective against, e.g., the Feline Calicivirus (an EPA approvedsurrogate for Norovirus), Methicillin Resistant Staphylococcus Aureus(MRSA), Vancomyacin Resistant Enterococcus Faecalis (VRE), ClostridiumDifficile (C-Diff), Geobacillus Stearothermophilus, and AspergillusNiger. Such amounts of PHPG are safe to use in occupied areas(including, but not limited to, schools, hospitals, offices, homes, andother common areas), disinfect surface contaminating microbes, killairborne pathogens, and provide microbial control, e.g., for preventingthe spread of Pandemic Flu, controlling nosocomial infections, andreducing the transmission of common illnesses.

In certain aspects of the invention, the humidity of the ambient air ispreferably above about 1% relative humidity (RH), above about 5% RH,above about 10% RH, etc. In certain embodiments, the humidity of theambient air may be between about 10% and about 99% RH. In oneembodiment, the method of the invention includes regulating the humidityof the ambient air within the range of about 5% to about 99% RH, orabout 10 to about 99% RH.

The metal, or metal oxide, catalyst may be selected from titaniumdioxide, copper, copper oxide, zinc, zinc oxide, iron, and iron oxide ormixtures thereof, and more preferably, the catalyst is titanium dioxide.More particularly, titanium dioxide is a semiconductor, absorbing lightin the near ultraviolet portion of the electromagnetic spectrum.Titanium dioxide is synthesized in two forms—anatase and rutile—whichare, in actuality, different planes of the same parent crystalstructure. The form taken is a function of the preparation method andthe starting material used. Anatase absorbs photons at wavelengths lessthan 380 nm, whereas rutile absorbs photons at wavelengths less than 405nm.

A layer of titanium dioxide approximately 4 μm thick will absorb 100% ofincident low wavelength light. Titanium dioxide is known to haveapproximately 9-14×10¹⁴ active surface sites per square centimeter. Anactive surface site is a coordinatively unsaturated site on the surfacewhich is capable of bonding with hydroxyl ions or other basic species.Its photocatalytic activity is influenced by its structure (anatase orrutile), surface area, size distribution, porosity, and the density ofhydroxyl groups on its surface. Anatase is generally considered to amore active photocatalyst than rutile. It is known to adsorb dioxygenmore strongly than rutile and remains photoconductive longer after flashirradiation than rutile. Anatase and rutile have band gap energies of3.2 and 3.0 electron volts (eV), respectively.

Numerous agents have been shown to have an influence on photocatalysis.Such agents may be added to the reaction environment to influence thephotocatalysis process. As recognized by those skilled in the art, someagents enhance the process, while others degrade it. Still others act toenhance one reaction while inhibiting another.

From acid-base chemistry, it has been found that basic agents may bondat the active site on the catalyst. Without being limited by theory,reducible agents which adsorb on the catalyst more strongly thandioxygen may substitute as the electron acceptor. Small moleculechemicals, metals, and ions have all shown this capability. In thesecases, the impact on formation of PHPG are dictated by the efficiencywith which the agent accepts electrons relative to dioxygen and hydrogenperoxide.

Some additive agents involve radical species in side reactions or in theformation of less reactive radicals incapable of performing the desiredreaction. Yet others physically alter the photocatalyst, changing itsperformance. In accordance with the present invention, additive agentsmay be selected to optimize the formation of PHPG (optionally whileminimizing or eliminating the formation of ozone, plasma species, ororganic species).

In one aspect, as mentioned above, additive agents may includeco-catalysts. Co-catalysts may be metals or coatings deposited on thesurface of a catalyst to improve the efficiency of selected PHPGreactions. Cocatalysts may alter the physical characteristics ofcatalyst in two ways. First, they may provide new energy levels forconduction band electrons to occupy. Second, co-catalysts may possessdifferent absorption characteristics than the supporting photocatalyst.This may cause the order in which competing reactions take place on theco-catalyst to be different from that on the catalyst itself.Cocatalysts are generally most effective at surface coverages of lessthan five percent.

Typical co-catalysts may be selected from platinum, silver, nickel,palladium, and many other metal compounds. Phthalocyanine has alsodemonstrated cocatalytic capabilities.

A diffuser apparatus in accordance with the invention may be of anysuitable shape or size, including spherical, hemispherical, cubic, threedimensional rectangular, etc. Diffusers may also be configured in anynumber of fanciful shapes such as teddy bears, piggy banks, mockradio's, etc. The core of the diffuser apparatus may be comprised of anultraviolet light source. The ultraviolet light source 4 may bepositioned at the center, or interior, of the diffuser apparatus, may beof varied intensity depending on the size of the apparatus and theapplication for which it is intended. By way of example, In certainembodiments, with reference to FIG. 1, the ultraviolet source 4, e.g.,may be tubular in shape may be contained within an elongatedwedge-shaped, or tube shaped diffuser shell 2. In certain configurationsa reflector 1 may serve to focus light in a specific direction withinthe interior of a device as required by its specific shape.

The shell 2 of the diffuser apparatus may be formed from any suitablesubstrate material, including ceramic, porcelain, polymer, etc. By wayof example, the polymer may be a porous or vented polymer that is bothhydrophobic and resistant to degradation by ultraviolet light in the 254nm to 182 nm range. Polymers that are resistant to some wavelengthswithin this range, but not all, may be used in conjunction with UV lampsthat only produce light in the ranges to which they are resistant. Adiffuser shell may be molded into any desired size and shape, and formedas any color desired. In certain embodiments, a phosphorescent materialmay be incorporated into the shell material so as to emit visible lightupon absorption of UV light.

In one embodiment, the interior surface of the diffuser shell maygenerally be used as the substrate by coating it with photocatalyst,which may include titanium dioxide doped with one or more other metalsin certain embodiments. By way of example, the photocatalyst may beapplied to the interior of the diffuser substrate as a paint. Theapplication should generally be applied so as to prevent clogging of thepores within the diffuser substrate. In one embodiment, air may beapplied to the substrate, and forced through the pores of the substrateafter application of the photocatalyst paint, both causing the coatingto dry and keeping the pores clear by means of forced air. It may bepreferred for the combination of photocatalytic coating and diffusersubstrate to be opaque enough to prevent UV light from escaping theassembled diffuser apparatus.

In another embodiment, the diffuser shell and the catalyst substrate areseparate components, with the substrate layer situated just inside, andvery close to, the interior surface of the diffuser shell.

The diffuser design optimizes PHPG production by spreading the airpermeable photocatalytic reactor surface thinly over a large area thatis perpendicular to air flow, rather than by compacting it into avolume-optimizing morphology designed to maximize residence time withinthe reactor. By configuring the reactor morphology as a thin, sail-likeair-permeable structure, just inside the diffuser's interior shell, theexit path length for hydrogen peroxide molecules produced on thecatalyst becomes very short, and their residence time within the reactorstructure is reduced to a fraction of a second, preventing the vastmajority of hydrogen peroxide molecules from being subsequently adsorbedonto the catalyst and reduced back into water. Also, by placing thecatalyst substrate just inside the interior surface of the diffusershell, not only is reactor surface area maximized, but the PHPG producedalso passes out of the diffuser almost immediately and thus avoidsphotolysis from prolonged exposure to the UV light source. By means ofthis morphology, PHPG output concentrations as high as 0.08 ppm havebeen achieved.

In preferred embodiments, PHPG concentrations maybe self-regulating dueto the electrostatic attraction between PHPG molecules, which degrade towater and oxygen upon reacting with each other. PHPG self-regulationoccurs whenever the concentration of PHPG results in intermolecularspacing that is closer in distance than the electrostatic attractionrange of the PHPG molecules. When this occurs, PHPG molecules areattracted to, and degrade each other until the concentration dropssufficiently that the intermolecular spacing is greater than theelectrostatic attraction range of the PHPG molecules. By this means PHPGconcentrations are maintained at levels well below the OSHA workplacesafety limit of 1.0 parts per million.

It should be noted that this PHPG optimizing morphology also minimizesthe residence time for any organic contaminants that may enter and passthrough the system, dramatically reducing the probability that they willbe oxidized. Effectively, photocatalytic systems optimized for PHPGproduction, are, by design, less likely to oxidize organic contaminantsas they pass through the catalyst structure; and photocatalytic systemsoptimized for the oxidation of organic contaminants will, by design,inhibit hydrogen peroxide gas production.

The diffuser apparatus also generally includes a fluid distributionmechanism. The fluid distribution mechanism generally serves to movefluid, such as air through the diffuser apparatus. More particularly,the air distribution mechanism will generally direct fluid into thediffuser apparatus, which will then diffuse out through the diffusersubstrate. In one embodiment, with reference to FIG. 2, the fluiddistribution mechanism will direct fluid through an intake vent 7 to asmall fan (not shown) framed within an opening 5 in the diffuserapparatus. The fan may also have a replaceable hydrophobic gas and/ordust filter 6 on the upstream side to prevent organic gases and/or dustfrom entering the diffuser apparatus, thus ensuring that the PHPGremains substantially free of organic species. Based on need, in certainembodiments, it may be desirable for the fluid distribution mechanism tobe of the lowest power necessary to create a gentle overpressure withinthe diffuser; in other embodiments, a rapid fan speed may be moredesirable.

In accordance with certain aspects of the invention, PHPG may beproduced in the substantial absence of ozone, plasma species, and/ororganic species, e.g., by the photocatalytic oxidation of adsorbed watermolecules when activated with UV light in the ranges described herein.In one embodiment, the diffuser substrate, coated with photocatalyst onits interior (or diffuser shell lined on the interior with a thinsail-like air-permeable photocatalyst structure), may be placed over andaround the ultraviolet lamp. An opening in the diffuser may serve as aframe into which the UV light's power source and structural support willfit. When assembled, the diffuser apparatus may function as follows: (a)the fluid distribution mechanism directs air into the diffuser throughan organic vapor and dust filter, creating an overpressure; (b) airmoves out of the diffuser through the pores or vents in the substrateand/or diffuser shell; (c) moisture contained in the air adsorbs ontothe photocatalyst; (d) when illuminated, the UV light produced by thelamp activates the photocatalyst, causing it to oxidize adsorbed waterand reduce adsorbed oxygen, producing PHPG; and (e) the PHPG produced inthe interior of the diffuser apparatus then moves rapidly out of thediffuser through its pores or vents into the surrounding environment.

In some embodiments, PHPG may be generated by a Medium Pressure MercuryArc (MPMA) Lamp. MPMA lamps emit not only ultraviolet light, but alsovisible light, and wavelengths in the infrared spectrum. It is importantthat when selecting a lamp, output in the ultraviolet spectrum should beclosely examined. The ultraviolet spectral output is sometimes expressedgraphically, showing the proportional output at the importantultraviolet wavelengths. The broad spectrum of the MPMA lamp is selectedfor its functionality.

In other embodiments, PHPG may be generated by Ultraviolet LightEmitting Diodes (UV LED's). UV LED's are more compact and banks of UVLED's can be arrayed in a variety of sizes and ways, enabling theproduction of smaller, more rugged systems.

In other embodiments, PHPG output may be regulated by control systemsmanaging devices singly, or in groups. Such control systems may regulateoperation by: (a) turning devices on and off; (b) regulating lightintensity and/or fan speed; (c) monitoring ambient PHPG levels directlyby means of automated colorimetric devices, by automated Draegerindicators, by means of flash vaporization of PHPG accumulated in anaqueous trap, by measuring the change in conductivity of a substratesensitive to hydrogen peroxide accumulation, or by thermal means,measuring the heat evolved by the exothermic reaction between PHPG and astable reactant to which it is electrostatically attracted; and (d)monitoring ambient PHPG levels indirectly through relative humidity.

EXAMPLES

Without intent to be limited by the following performance example, oneembodiment of the invention was constructed as follows: (a) the devicewas constructed in the shape of a quarter-cylinder 20 inches in length,and with a radius of 8.5 inches; (b) the quarter cylinder was designedto fit into the 90 degree angle formed where a wall meets a ceiling,with the quarter-cylinder's straight sides fitting flush against thewall and ceiling, and the curved face of the cylinder facing out anddown into the room; (c) as viewed from below, the right end of thequarter-cylinder supported a variable speed fan with a maximum output of240 cubic feet per minute, and a high efficiency, hydrophobic, activatedcharcoal intake filter; (d) the left end of the quarter cylindersupported the power connection for the fan, and a fourteen inch MediumPressure Mercury Arc (MPMA) lamp, positioned so that the lamp wascentered within, and parallel to, the length of the quarter-cylinder;(e) a vented metal reflector was placed behind the MPMA lamp to reflectlight toward the interior surface of the curved face of thequarter-cylinder; and (0 the curved face of the cylinder was vented toallow air, but not light, to flow out of the device.

A curved sail-like photocatalyst structure was placed just inside, andparallel to, the interior surface of the curved face of thequarter-cylinder; (a) the catalyst substrate was eighteen inches long,eleven inches high, framed, and had a curvature from top to bottom witha radius of 8.25 inches; (b) was formed of fiberglass, and was coatedwith crystalline titanium dioxide powder; and (c) the titanium dioxidewas applied to the fiberglass in five coats to ensure complete coverageof all fibers, then sintered in an oven to cause the photocatalystcrystals to bond both to each other and to the fiberglass.

During operation, both the fan and the MPMA lamp were turned on: (a)intake air was drawn into the device through the high efficiency,hydrophobic, activated charcoal intake filter which removed byadsorption Volatile Organic hydroCarbons (VOC's), without removingmoisture from the intake air; (b) the intake air was supplied to theback of the device, where the vented metal reflector redirected itevenly toward the photocatalyst structure, and the interior of thevented face of the quarter-cylinder; (c) moisture and oxygen from theintake air adsorbed onto the photocatalyst, which was activated by 254nm light from the MPMA lamp; (d) the activated photocatalyst oxidizedwater to hydroxyl radicals, which then combined to form hydrogenperoxide, while dioxygen was simultaneously reduced on the photocatalystto hydrogen peroxide; and (e) the Purified Hydrogen Peroxide Gas (PHPG)generated was immediately carried by the air flow off of thephotocatalyst, through the light-impermeable vented face of the device,and out into the room.

The Purified Hydrogen Peroxide Gas (PHPG) thus produced was: (a)substantially free of bonded water because it was produced by catalyticmeans rather than by the vaporization of aqueous solution; (b) the PHPGwas substantially free of ozone because the MPMA lamp did not use anywavelengths capable of photolyzing dioxygen; (c) the PHPG wassubstantially free of plasma species because the morphology of thephotocatalyst permitted the rapid removal of hydrogen peroxide from itssurface before it could subsequently be reduced photocatalytically; (d)the PHPG was protected from Ultraviolet (UV) photolysis because itpassed out through the light-impermeable, vented face of thequarter-cylinder immediately upon exiting the photocatalyst surface; and(e) the PHPG was substantially free of organic species because VOC'swere adsorbed by the high efficiency, hydrophobic, activated charcoalintake filter.

The device was subjected to tests designed and implemented by twoaccredited laboratories to: (a) measure the output of Purified HydrogenPeroxide Gas (PHPG); (b) confirm that the output was substantially freeof ozone; (c) confirm that the output was substantially free of VOC's;(d) measure the efficacy of PHPG against the Feline Calicivirus (anEPA-approved substitute for noroviruses), Methicillin ResistantStaphylococcus aureus (MRSA), Vancomyacin Resistant Enterococcusfaecalis (VRE), Clostridium difficile (C-Diff), Geobacillusstearothermophilus, (a stable bacteria used by the insurance industry toverify successful microbial remediation), and Aspergillus niger (acommon fungus); and (e) test at a variety of ambient relative humiditiesincluding 35% to 40% at 70 to 72 degrees Fahrenheit, 56% to 59% at 81 to85 degrees Fahrenheit, and 98% at 78 degrees Fahrenheit.

Measurements for ozone, VOC's, temperature, and humidity were allaccomplished using standard devices. Since no device is yet readilyavailable to measure hydrogen peroxide gas at levels below 0.10 ppm,three new means were devised: (a) hydrogen peroxide test strips,normally used to measure approximate concentrations in aqueous solution,were found to detect the presence of PHPG over time; (b) hydrogenperoxide test strips, normally designed to be read after 20 seconds ofexposure, were found to accumulate PHPG, and to provide approximatereadings of PHPG concentration accurate to within 0.01 ppm, whennormalized for exposure time over periods of less than an hour—forexample, a test strip that accumulated 0.5 ppm over the course of fiveminutes was exposed for 15 twenty-second intervals, indicating anapproximate concentration of 0.5 ppm divided by 15, or 0.033 ppm; (c)Draeger tubes, designed to detect hydrogen peroxide concentrations aslow as 0.10 ppm after drawing 2000 cubic centimeters of air, were foundto provide readings of lower concentrations accurate within 0.005 ppm,as larger volumes were drawn by a calibrated pump—for example, a Draegertube that indicated 0.10 ppm after drawing 4000 cubic centimetersmeasured an approximate PHPG concentration of 0.05 ppm, and a Draegertube that indicated 0.10 ppm after drawing 6000 cubic centimeters,measured an approximate PHPG concentration of 0.033 ppm; and (d)measurements taken with both hydrogen peroxide test strips and Draegertubes were found to closely agree with each other.

In tests designed to measure hydrogen peroxide levels at varyinghumidities, the following data was collected:

Relative Temperature PHPG Means of Humidity (Fahrenheit) ConcentrationDetection/Measurement 98% 78 0.08 ppm Test strip/Draeger tube/ Microbialreduction 56%-59% 81-85 0.05-0.08 ppm Test strip/Draeger tube/ Microbialreduction 35%-40% 70-72 0.005-0.01 ppm Test strip/Microbial reduction

The PHPG measurement data indicated that the concentration of PHPGproduced is highly dependent on the relative humidity. This ispredictable, because the production of PHPG is directly dependent on theavailability of water molecules in the air. It should be noted that theUS Department of Health and Human Services requires that hospitaloperating rooms be maintained between 30% and 60% relative humidity.

The PHPG measurement data also remained constant over time and indicatedan upper equilibrium limit of approximately 0.08 ppm. This is alsopredictable due to the electrostatic attraction of PHPG molecules toeach other whenever their intermolecular spacing becomes less than theirmutual electrostatic attraction ranges. Under this condition excess PHPGreacts with itself to produce oxygen and water molecules. This upperlimit of 0.08 ppm is also well below the OSHA workplace safety limit of1.0 ppm and thus safe to breathe, indicating that PHPG systems can besafely and continuously used in occupied areas.

All testing also indicated a complete absence of ozone in the device'soutput.

In VOC testing, an approximate ambient concentration of 7 ppm of2-propanol was established 2500 cubic foot room. The device was found torapidly reduce VOC levels throughout the room.

VOC (ppm) H₂O₂ (ppm)-Draeger Ozone ppm Station: 1 2 3 4 5 Distance 2″ 9′12′ 16′ 20′ Zero Time 6.8 7.0 6.8 6.8 6.7 Units Light and fan (high)turned on 5 min 6.0 5.7 5.6 5.6 5.6 10 min 4.2 4.4 3.7 3.9 3.6 15 min3.6 3.6 3.1 3.1 2.9 30 min 1.2 1.3 1.1 1.1 1.1 60 min 0.4 0.6 0.9 0.40.2 0.05 at room center 90 min 0.1 0.4 0.5 0.3 0.2 0.000 all St 24 hr0.0 0.0 0.0 0.0 0.0 0.08 at center & S-5 0.000 all St

In qualitative microbial testing, chips inoculated with Geobacillusstearothermophilus were placed in the environment in several tests, andin all cases showed significant reduction of the bacteria within amatter of hours.

In quantitative microbial testing at ATS labs in Eagan, Minn. thefollowing data was collected. It should be noted that these impressivekill rates were achieved with a PHPG concentration of just 0.005 ppm to0.01 ppm, produced at a relative humidity of 35% to 40%.

Percent Average Virus Reduction as Percent Reduction ExposureInfectivity Compared to Compared to Test Time Observed Time ZeroCorresponding Organism (hrs) After Exposure Virus Control NaturalDie-off Feline 2 4.3 log₁₀ 99.5% 96.8% Calicivirus 6 2.3 log₁₀ 99.995%99.8% (Norovirus 24 ≤0.6 log₁₀ (virus ≥99.9999% 99.8% substitute)detected in only one replicate) Percent Reduction as Percent ReductionAverage CFU/Test Compared to Compared to Test carrier Time ZeroCorresponding Organism Time point (Survivors in the test) ControlNatural Die-off MRSA 2 hours <1 (no survivors) >99.9999% >99.9999% (ATCC33592) 6 hours <1 (no survivors) >99.9999% >99.9999% 24 hours <1 (nosurvivors) >99.9999% >99.9999% VRE 2 hours <1 (nosurvivors) >99.9999% >99.999% (ATCC 51575) 6 hours <1 (nosurvivors) >99.9999% >99.99% 24 hours <1 (no survivors) >99.9999% >99.9%C. difficile 2 hours 2.18 × 10⁵ CFU/ 27.3% 9.2% (ATCC 700792) Carrier 6hours 1.1 × 10⁵ CFU/ 63.3% 60.6% Carrier 24 hours 7.3 × 10⁴ CFU/ 75.7%70.4% Carrier A. niger 2 hours 1.9 × 10⁵ CFU/ 19.1% 13.6% (ATCC 16404)Carrier 6 hours 4.67 × 10⁴ CFU/ 80.1% 81.3% Carrier 24 hours 1.2 × 10⁴CFU/ 94.9% 90.8% Carrier

At higher humidities, higher concentrations of PHPG are produced, andmicrobial reduction rates will increase. The data collected above at 56%to 59% relative humidity indicates that a PHPG concentration at leasteight times higher than used in this quantitative test can be achieved.

Also, a comparison test indicated that the PHPG test device produces aPHPG equilibrium concentration up to 150 times greater than theincidental output of unpurified hydrogen peroxide from a standardphotocatalytic cell.

Generally, the invention has been described in specific embodiments withsome degree of particularity, it is to be understood that thisdescription has been given only by way of example and that numerouschanges in the details of construction, fabrication and use, includingthe combination and arrangement of parts, may be made without departingfrom the spirit and scope of the invention.

1-15. (canceled)
 16. A method for microbial control of an environment,the method comprising: (a) exposing a metal or metal oxide comprisingtitanium oxide to ultraviolet light above 187 nanometers (nm) and lessthan 405 nm in the presence of a flow of ambient air to form anon-hydrated hydrogen peroxide gas; (b) directing said non-hydratedhydrogen peroxide gas into said environment to prepare an environmentcomprising non-hydrated hydrogen peroxide gas and an ozone concentrationof less than 0.1 parts-per-million (ppm); wherein said microbial controlis reduction of a virus, bacterium, or fungus, in said environment. 17.The method according to claim 16, wherein said metal or metal oxidecomprises the anatase form of titanium oxide.
 18. The method accordingto claim 16, wherein said ultraviolet light is less than 380 nm.
 19. Themethod according to claim 16, wherein said microbial control comprisesmicrobial reduction of viruses, bacteria, or fungi, on surfaces in saidenvironment.
 20. The method of claim 16, wherein said microbial controlis for a period of at least 2 hours.
 21. The method according to claim16, wherein said ultraviolet light is provided by one or moreUltraviolet Light Emitting Diodes (UV LEDs).
 22. The method according toclaim 16, wherein non-hydrated hydrogen peroxide gas is present in saidenvironment at a concentration between 0.005 ppm to 0.1 ppm.
 23. Themethod according to claim 16, wherein said ozone concentration in saidenvironment is less than 0.015 ppm.
 24. A method for microbial controlof an environment, the method comprising: a. exposing a metal or metaloxide comprising titanium oxide to ultraviolet light above 187nanometers (nm) and less than 405 nm in the presence of ambient air toform a plasma; b. directing a flow of air through the plasma to producea non-hydrated hydrogen peroxide gas; c. directing said non-hydratedhydrogen peroxide gas into said environment wherein said non-hydratedhydrogen peroxide gas comprises an ozone concentration of less 0.1parts-per-million (ppm) ozone and is free of plasma species; and d.controlling microbes on surfaces in said environment.
 25. The methodaccording to claim 24, wherein said metal or metal oxide comprises theanatase form of titanium oxide.
 26. The method according to claim 24,wherein said ultraviolet light is less than 380 nm.
 27. The methodaccording to claim 24, wherein said ozone concentration in saidenvironment is less than 0.015 ppm.
 28. The method of claim 24, whereinsaid ultraviolet light is provided by one or more Ultraviolet LightEmitting Diodes (UV LED's).
 29. The method of claim 24, wherein saidcontrolling microbes on surfaces in said environment comprises reductionof virus infectivity or a reduction in the average number of colonyforming units of a bacteria.
 30. The method according to claim 24,wherein non-hydrated hydrogen peroxide gas is present in saidenvironment at a concentration between 0.005 ppm to 0.1 ppm.
 31. Amethod of microbial control comprising: a. providing a flow of humidambient air to a photocatalytic cell comprising a titanium dioxidecatalyst in the anatase form; b. irradiating said titanium dioxidecatalyst with ultraviolet (UV) light above 187 nanometers (nm) togenerate Purified Hydrogen Peroxide Gas (PHPG) that is free ofhydration; c. directing said PHPG into an environment to maintain a PHPGconcentration of between 0.005 parts-per-million (ppm) and 0.1 ppm andcomprises less than 0.1 ppm ozone; and d. controlling said microbes. 32.The method of microbial control of claim 31, wherein said ultravioletlight has a wavelength below 405 nanometers (nm) and is provided by oneor more Ultraviolet Light Emitting Diodes (UV LED's).
 33. The method ofmicrobial control of claim 31, wherein said PHPG is between 0.02 ppm and0.05 ppm.
 34. The method of microbial control of claim 31, wherein saidenvironment comprises less than 0.015 ppm ozone.
 35. The method ofmicrobial control of claim 31, wherein said controlling microbescomprises reduction of virus infectivity or a reduction in the averagenumber of colony forming units of a bacteria.
 36. The method ofmicrobial control of claim 31, wherein said microbe is a bacterium. 37.The method of microbial control of claim 35, wherein said microbe isFeline Calicivirus, Staphylococcus aureus, Enterococcus faecalis,Clostridium difficile, Geobacillus stearothermophilus, or AspergillusNiger.